The present invention relates to hermetic fiber ferrules and feedthroughs and a method for making hermetic fiber ferrules and feedthroughs.
Optical fibers are used in a wide variety of applications ranging from telecommunications to medical technology and optical components.
It is desirable to hermetically seal optical devices in a housing to prevent deterioration in performance due to moisture and other species present in the atmosphere. Furthermore, it is desirable to improve the reliability of optical fibers in hermetically sealed fiber ferrules and feedthroughs.
A number of fiber optic applications require optical fibers to be packaged in a ferrule, such as a metal, glass, or ceramic ferrule, so that the fiber tip can be aligned and fixed with respect to an optical component. For a variety of applications it is desirable that such a ferrule is a hermetic ferrule. Further, in certain applications it is necessary to bring an optical fiber into a sealed package which requires a hermetic fiber feedthrough. Herein arises the need for a satisfactory method to hermetically seal optical fibers within fittings or sleeves.
Device packages that incorporate an optical or opto-electronic component have an aperture for the feedthrough of the optical fibers that conduct light to or from the package. It has been usual practice to support the connecting portion of the fibers in a metal sleeve and then for the sleeve to be mounted in the aperture, the fibers being held in the sleeve by a metal solder or epoxy resin.
If a fiber is to be soldered into the sleeve it is common practice to metallize the fiber so that the metal solder will adhere to the fiber and the additional handling of the delicate fiber during the metallization process can cause damage.
An epoxy process, on the other hand, does not provide hermeticity as moisture and gases can diffuse through the epoxy adhesive. In addition, there is a slow release of gases from the resin (even after heat treatment) and the gases that are discharged can be harmful to components within the package.
U.S. Pat. No. 5,143,531 in the name of Kramer issued on Sep. 1, 1992 discloses a glass-to-glass hermetic sealing technique which can be used to splice lengths of glass fibers together. A solid glass pre-form is inserted into the cavity of a metal component which is then heated to melt the glass. An end of an optical fiber is then advanced into the molten glass and the entire structure is cooled to solidify the glass in sealing engagement with the optical fiber end and the metal cavity.
Another U.S. Pat. No. 5,337,387 in the name of the same inventor issued Aug. 9, 1994 and relates to a method of the continuous processing of hermetic fiber optic components and the resultant fiber optic-to-metal components by assembling and fixturing elements comprising a metal shell, a glass pre-form and a metal-coated fiber optic into desired relative positions and then sealing said fixtured elements, preferably using a continuous heating process.
U.S. Pat. No. 5,177,806 issued on Jan. 5, 1993 to Abbott et al. discloses an optical fiber feedthrough using a glass seal for sealing the optical fiber within the metal sleeve. The hermetic seal between the optical fiber and the feedthrough sleeve is accomplished utilizing the glass solder. The stripped fiber is fed through a capillary in the glass pre-form. During a subsequent heat treatment the pre-form is heated to its flow temperature so that it forms a seal between the fiber and the sleeve.
A bare optical fiber, stripped of its protective outer cover is particularly vulnerable to damage during manufacturing and assembly. This vulnerability increases fiber failures in the field and during operation which is the predominant failure mode of fiber ferrules and feedthroughs and hence raises the cost of operation and maintenance of an optical fiber system. The long-term reliability of an optical fiber is increasingly important with increasing bandwidth capability. Therefore, there is a need for a more robust optical fiber hermetic seal.
Methods are known for placing and affixing optical fibers in ferrules and sleeves of different types for the purpose of providing a protective sheath for reducing damage to optical fibers that would otherwise be exposed, and for attempting to provide a housing for optical fibers. Furthermore, a centering of stripped fibers within a capillary, as commonly done in the prior art, is a delicate task involving great risk of causing damage to the fiber. The small clearance between the sleeve and the fiber make it very difficult to insert the fiber without damage, such as scratches or nicks in the fiber, which will result in a weak joint and can eventually lead to fiber breakage.
It is an object of the present invention to provide a method for making a hermetic fiber ferrule and/or feedthrough using a novel glass solder process.
It is an object of the invention to provide a method for making a hermetic fiber ferrule and/or feedthrough based on an extrusion method.
It is a further object of the present invention to provide a reliable hermetic fiber ferrule and/or feedthrough utilizing a glass solder process.
In accordance with the invention there is provided, a hermetic fiber-optic seal comprising an optical fiber, a glass solder for encasing at least a portion of the optical fiber, a first glass sleeve for encasing at least a first portion of the glass solder, a second glass sleeve for encasing at least a second portion of the glass solder, and an outer sleeve for encasing at least a portion of the first glass sleeve and the second glass sleeve.
In accordance with an embodiment of the invention, the hermetic fiber-optic seal comprises a gap between the first glass sleeve and the second glass sleeve, said gap being filled with the glass solder.
In accordance with another aspect of the invention, there is provided, a method of hermetically sealing at least a portion of an optical fiber comprising the steps of providing a length of optical fiber, providing a first glass sleeve having a first bore therethrough, providing a second glass sleeve having a second bore therethrough, providing a glass solder pre-form having a third bore therethrough, said glass solder pre-from being disposed between the first glass sleeve and the second glass sleeve such that the first bore, the second bore, and the third bore are substantially aligned, providing an outer sleeve for encasing the glass solder pre-form and at least a portion of the first glass sleeve and the second glass sleeve, inserting said length of optical fiber through the substantially aligned first bore, second bore, and third bore, providing a pre-load to the first glass sleeve, the second glass sleeve, and the glass solder pre-form, and heating at least a portion of said outer sleeve for extruding the glass solder pre-form between the optical fiber and said first and second glass sleeve.
In accordance with another aspect of the invention a hermetic fiber ferrule is made in accordance with the method of the present invention.
In accordance with another aspect of the invention a hermetic fiber feedthrough is made in accordance with the method of the present invention.
In accordance with the invention there is further provided a hermetic fiber-optic ferrule comprising an optical fiber, a glass solder for encasing at least a portion of the optical fiber, a first glass sleeve for encasing at least a first portion of the glass solder, and an outer sleeve for encasing at least a portion of the first glass sleeve.
In accordance with an embodiment of the invention, the hermetic fiber-optic ferrule further comprises a second glass sleeve for encasing at least a second portion of the glass solder, said outer sleeve further encasing at least a portion of the second glass sleeve.
Advantageously, the present invention uses a pre-load to extrude glass solder pre-form through the sleeves. This enables the use of a relatively loose tolerance (inexpensive), large internal diameter (ID) solder glass pre-form and glass sleeves. The large ID, apart from facilitating an easy insertion, is further important in that it avoids abrasion damage to the fiber and thus increasing the strength and joint reliability of the hermetic fiber optic seal.
The present invention further allows a polishing of the fiber terminus, in the case of ferrule application, with ease, wherein one end of the hermetic fiber ferule is polished to a given specification.
A further advantage of the present invention is that the use of glass sleeves reduces thermal damage to the polymer buffer in the case of feedthrough and ferrule applications.
The application of a small tension to the fiber is advantageously employed to counter wetting forces which tend to de-center the fiber.